The long-term objective of this proposal is to apply a powerful new "covalent tethering" technology to the discovery of novel therapeutics that inhibit HIV integrase for the treatment of AIDS. Although drugs that block HIV integrase activity would strongly complement the existing arsenal of anti-HIV therapeutics, the discovery of lead compounds using traditional methods has thus far been largely unsuccessful. Covalent tethering technology involves the discovery of drug-like "fragments" that bind to a protein target, followed by their assembly by chemical linkage into potent inhibitors. This "screen-then-link" process is much more efficient and offers a greater survey of chemical diversity space than the typical lead discovery paradigm, in which large compound libraries are first created and then screened in a functional assay. Covalent tethering relies on the selective capture of sulfhydryl-containing fragment molecules on cysteine residues introduced on the surface of a target protein. We propose to conduct a full survey of the HIV integrase active site surface by screening a series of cysteine mutants versus our custom library of >I 0,000 sulfhydryl-containing inhibitor fragments. For promising fragments, disulfide tethers will be removed and appropriate combinations will be fused using structure-base design, to generate compounds that bind non-covalently and serve as starting points for medicinal chemistry.